Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 7 Jun 2018 10:32:29 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Daniel Lezcano <daniel.lezcano@linaro.org>
Cc:     rjw@rjwysocki.net, linux-kernel@vger.kernel.org,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Eduardo Valentin <edubezval@gmail.com>,
        Javi Merino <javi.merino@kernel.org>,
        Leo Yan <leo.yan@linaro.org>,
        Kevin Wangtao <kevin.wangtao@linaro.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Rui Zhang <rui.zhang@intel.com>,
        Daniel Thompson <daniel.thompson@linaro.org>,
        "open list:POWER MANAGEMENT CORE" <linux-pm@vger.kernel.org>
Subject: Re: [PATCH V5] powercap/drivers/idle_injection: Add an idle
 injection framework
Message-ID: <20180607083229.GJ12198@hirez.programming.kicks-ass.net>
References: <1528190208-22915-1-git-send-email-daniel.lezcano@linaro.org>
 <20180606122357.GN12258@hirez.programming.kicks-ass.net>
 <22f5cf0b-049e-7938-55f6-4b4b154f8389@linaro.org>
 <20180606150203.GE12180@hirez.programming.kicks-ass.net>
 <ea347237-7cef-095a-5ddb-19c181d10c23@linaro.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <ea347237-7cef-095a-5ddb-19c181d10c23@linaro.org>
User-Agent: Mutt/1.9.5 (2018-04-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Jun 07, 2018 at 10:18:27AM +0200, Daniel Lezcano wrote:
> So IIUC, neither atomic or WRITE|READ_ONCE are necessary in this code
> because of the wake_up_process() barrier is enough, right ?

I didn't look hard enough; if there ever is a time where the loads and
stores happen concurrently, you need READ/WRITE_ONCE(). If there is no
concurrency on the variables, you don't need anything.

Neither atomic_read/set() nor REAd/WRITE_ONCE() will help with ordering,
which is what the wake_up_process() would provide here, different things
entirely.